Your SlideShare is downloading. ×
Sorci Sess7 101309
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Sorci Sess7 101309

551
views

Published on

Published in: Technology

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
551
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Impact of Levee Cutoff Walls on Groundwater Recharge Presented By: Paul Sorci, PE
  • 2.  
  • 3.  
  • 4. Outline
    • Sacramento River Location
    • Overview of How and Why Cutoff Walls Work
    • How Cutoff Walls are Constructed
    • How Cutoff Walls Affect Groundwater
    • Summary
    • Questions
  • 5. Sacramento River Location Sacramento River Farmlands Downtown Sacramento Groundwater Analyzed
  • 6. Overview of Cutoff Walls
    • How They Work
      • Creates a nearly impermeable vertical element that stops water from traveling horizontally through permeable layers
      • Lowers the amount of pore pressure at the landside levee toe due to high water levels
  • 7. Overview of Cutoff Walls
    • How They Work
    Cutoff Wall Permeable Sands Fine Grained Soils Fine Grained Soils
  • 8. Overview of Cutoff Walls
    • How They Work
  • 9. Overview of Cutoff Walls
    • Multiple Methods of Installation in Natomas
      • Deep Soil Mixing
      • Slurry Trench Method
  • 10. Cutoff Wall Construction
    • Deep Soil Mix Method
    Permeable Sands Low Permeable Clay/Silt Levee/Blanket Layer Ground Surface 5’ Min. 6’ Wide Element 2’ Overlap
  • 11. Cutoff Wall Construction
    • Deep Soil Mix Method
    Previously Mixed Element Next Element Alignment Next Element
  • 12. Cutoff Wall Construction
    • Deep Soil Mix Method
    Slurry Injection at Auger Tips
  • 13. Cutoff Wall Construction
    • Slurry Trench Method
    Permeable Sands Low Permeable Clay/Silt Levee/Blanket Layer Ground Surface
  • 14. Cutoff Wall Construction
    • Slurry Trench Method
    Spoils Used for Mixing Consisting Mostly of Clay Excavated Trench Bentonite Slurry
  • 15. Cutoff Wall Construction
    • Slurry Trench Method
    Mixing Excavator Bentonite Slurry Mix of Soil, Cement, and Bentonite
  • 16. Cutoff Wall Construction
    • Slurry Trench Method
    Trench Backfill Trench Mix
  • 17. Cutoff Wall Construction
    • Compare and Contrast
      • DSM
        • Mixes in situ soils – less spoils
        • Smaller construction footprint – less equipment
      • Slurry Trench
        • Allows engineer to see material wall is keying in
        • Better quality control
  • 18. Groundwater Affects
    • Problem
      • Soil bentonite (cutoff) walls will reduce groundwater recharge to landside of levee
      • Perform seepage analysis to evaluate
        • Estimate groundwater flow with and without cutoff wall in place
        • Estimate effect of nearby canals on groundwater recharge
  • 19. Groundwater Affects
    • Two Types of Anlaysis
      • Steady State
      • Transient
      • Did not account for 3-D effects i.e. flow around edges of cutoff wall
      • Use hydrograph to perform transient analysis
  • 20. Groundwater Affects
    • Parameters Selected
      • Permeability Modeled as 10 -6 cm/sec
      • Stratigraphy Different at Sections
        • Wall extends 5 feet into fine grained foundation
        • Material beneath wall either sand or clay depending on stratigraphy
        • Cutoff wall less effective when sand beneath wall
  • 21. Groundwater Affects
    • Steady State Seepage Analysis
      • Stations 70+00 cutoff wall fully penetrates sand layer
      • Station 353+00 cutoff wall only partially penetrates sand layer
      • Aquifer only recharges when river level above groundwater level
  • 22. Groundwater Affects
    • Steady State Seepage Analysis (cont)
      • Cutoff wall reduces seepage quantities up to 85 percent when sand layer is fully penetrated (Station 70+00)
      • Cutoff wall reduces seepage quantities up to 40 percent when sand layer is partially penetrated (Station 353+00)
  • 23. Station 70+00 85% Reduction Station 353+00 40% Reduction Cutoff Wall Tip in Fine Grained Soils Cutoff Wall Tip in Coarse Grained Soils
  • 24. Groundwater Affects
    • Transient Seepage
      • Verify and validate steady state seepage
      • Hydrograph used to create transient time steps
    Rainy Season – Groundwater Recharge
  • 25. Groundwater Affects
    • Transient Seepage
      • Analysis performed where sand layer is fully penetrated (Station 70+00)
        • Highest reduction in groundwater seepage
      • Cutoff wall reduces seepage quantities up to 70 percent, as compared to 85 percent for steady state seepage
      • Steady state seepage can conservatively approximate the effect of the cutoff wall
  • 26. Groundwater Affects
      • Overall, the cutoff wall will reduce groundwater aquifer recharge by about 20-25 percent
      • Effect may be lower due to 3-D flow
    Difference in Groundwater Recharge Rainy Season
  • 27. Groundwater Affects
    • Canals
      • Canal modeled about 800 feet from landside toe of levee
      • Time dependent boundary condition
      • Canal contained 5 feet of water from May to November
      • Canal empty December to April
  • 28. Groundwater Affects
    • Canals
      • Minimal impact of canal on groundwater elevations
      • Groundwater around cutoff wall increases in summer months
        • Due to water flow in canal and decrease of recharge to aquifer from the cutoff wall
  • 29. Summary
    • Cutoff Walls
      • Creates a nearly impermeable vertical element that stops water from traveling horizontally through permeable layers
      • Have been installed using a Deep Soil Mixing or Slurry Trench Method in Natomas Basin
  • 30. Summary
    • Groundwater Affects
      • Steady state conservatively estimates recharge quantities
      • Locally, areas may see reduction in recharge up to 85 percent
      • Overall, recharge reduced 20 to 25 percent
      • Cutoff wall could impede seepage to river during summer months
      • Canal and cutoff wall may locally increase groundwater levels in summer months
  • 31. Questions ?

×